They might not have had many predators on land 365 million years ago. GIven plenty of land and food, they had the resources to thrive. This is a salamander fossil from the Early Cretaceous period. The vertebral column and four limbs are easily identifiable.

Evolution of Amphibians

Fossil evidence shows that amphibians evolved about 365 million years ago from a lobe-finned lungfish ancestor. As the earliest land vertebrates, they were highly successful. Some of them were much larger than today’s amphibians. For more than 100 million years, amphibians remained the dominant land vertebrates. Then some of them evolved into reptiles. Once reptiles appeared, with their amniotic eggs, they replaced amphibians as the dominant land vertebrates.

Ecology of Amphibians

Amphibians can be found in freshwater and moist terrestrial habitats throughout the world. The only continent without amphibians is Antarctica. Amphibians are especially numerous in temperate lakes and ponds and in tropical rainforests.

Amphibians as Prey and Predators

Amphibians are an important food source for animals such as birds, snakes, raccoons, and fish. Amphibians are also important predators. As larvae, they feed mainly on small aquatic animals such as waterinsects. They may also feed on algae. As adults, amphibians are completely
carnivorous
. They may catch and eat worms, snails, and insects, as the frog in
Figure
below
is doing. Unlike other amphibians, caecilians are
burrowers
. They use their head to dig in the soil, and they feed on earthworms and other annelids. Caecilians can be found in moist soil near rivers and streams in tropical regions.

Frog Predator. A frog eating its insect prey.

The Threat of Amphibian Extinction

Currently, almost one third of all amphibian species face the threat of extinction. The reasons include habitat loss, pollution, climate change, and the introduction of non-native species. Most of these problems are the result of human actions.

Amphibians have permeable skin that easily absorbs substances from the environment. This may explain why they seem to be especially sensitive to pollution. Monitoring the health and survival of amphibians may help people detect pollution early, before other organisms are affected.

Summary

Amphibians evolved about 365 million years ago from a lobe-finned fish ancestor.

As the earliest land vertebrates, amphibians were highly successful for more than 100 million years until reptiles took over as the dominant land vertebrates.

Amphibians are found throughout the world except in Antarctica and Greenland.

Amphibians are important prey for animals such as birds, snakes, and raccoons. They are important predators of insects, worms, and other invertebrates.

Up to one third of all amphibian species are at risk of extinction because of human actions, such as habitat destruction, climate change, and pollution.